The present invention relates to catalysts and methods of steam reforming of a hydrocarbon.
Steam reforming of hydrocarbons is commonly used for feedstock production for carbon-monoxide hydrogenation (Fischer-Tropsch synthesis), methanol synthesis and hydrogen production. Steam reforming is done commercially by flowing a mixture of steam and the hydrocarbon past a supported catalyst having an alumina support and a catalyst metal thereon, and reacting the mixture at a temperature from about 600xc2x0 C. to about 1000xc2x0 C., forming at least one product. Research has been done with the catalyst metal on many types of supports, including a spinel support. Residence times for conventional processes are typically on the order of seconds and steam to carbon ratio greater than about 2.5. For steam to carbon ratio less than 2.5, catalyst activity is generally degraded after hours to days due to coke formation and the supported catalyst must be refreshed or replaced.
The rate of supported catalyst activity degradation has been reduced in conventional processes by use of excess steam (steam to carbon ratio greater than 2.5). Excess steam, however, requires excess thermal energy and may result in a large system pressure drop. Using less steam results in faster degradation of catalyst activity because of coking from the hydrocarbon(s).
Hence, there is a need for a method of steam reforming of a hydrocarbon that provides greater product yield and permits using less steam and maintaining catalytic activity of the catalyst.
The present invention provides a method of steam reforming, comprising: passing steam and hydrocarbon through a reaction chamber; wherein the reaction chamber comprises a spinel-containing catalyst that has surface active sites comprising a material selected from the group consisting of rhodium, iridium, nickel, palladium, platinum, ruthenium, carbide of group VIb and combinations thereof; wherein the rate of passing steam and hydrocarbon is controlled such that residence time in the reaction chamber is less than 0.1 seconds; wherein the temperature in the reaction chamber is in the range of 500xc2x0 C. to 1000xc2x0 C.; and wherein, after passing through the reaction chamber, at least 60% of the hydrocarbon has been converted to products after passing through the reaction chamber. xe2x80x9cConverted to productsxe2x80x9d simply means that the hydrocarbon has been reacted and changed its chemical formula (e.g., methane has been converted to CO and hydrogen).
The invention also provides a catalyst, that includes: (a) a first porous structure with a first pore surface area and a first pore size of at least about 0.1 xcexcm; (b) a porous interfacial layer that comprises a spinel with a second pore surface area and a second pore size less than said first pore size, said porous interfacial layer having a thickness less than 4 mm disposed upon said porous structure; and (c) a steam reforming catalyst that contains rhodium, iridium, nickel, palladium, platinum, ruthenium, carbide of group VIb and/or combinations thereof disposed upon the second pore surface area.
The invention also provides a catalyst that includes: an alumina layer; a metal exposed on the surface of the catalyst; and a spinel layer disposed between the alumina layer and the metal. The spinel layer is in direct contact with the alumina layer, and the metal includes a metal selected from the group consisting of: rhodium, iridium, nickel, platinum, palladium, and ruthenium. By xe2x80x9cexposed on the surfacexe2x80x9d it is meant that the metal would be exposed to reactant gases that contact the catalyst; the metal can be located inside pores and crevices as well as the very exterior of the catalyst.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.